iteration 2 of prusa mendel and x smooth rods.

Hi, I plan to build a prusa iteration 2, I already have a prusa by makergear, and I have printed all the printed parts, but, before the assembling, I have build it in blender with the stls, but I had to cut the smooth rods for X at 376 mm instead of the 420 mm of the wiki page. Is it correct ? Or did I miss something ? It's not finish, I have some nuts and blots to had and the extruder and hot-end, but it's almost done.

I think the 420 mm is from the original Prusa. 420 mm rods stick out a fair bit from the x-ends when everything is spaced at the recommended distances.

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Nice! I hope you will upload the blender file to the wiki. The smooth rods for the y-axis is on top of the threaded rods instead of being under it in iteration 2 or the bed won't clear the frame.

I asked prusajr at IRC today and he said 405 mm for the x axis smooth rods works.

ok, many thanks, I have almost finish a "low-poly" version, it only miss three or two M3 bolts, and nuts, and the washers. I will upload it if it's not to heavy.

I am building an iteration 2 now and noticed the same thing.

Since I don't have the ability to cut rods with any kind of precision, I added another set of nuts and spaced out the Z motor holders to match the extra length. The Z smooth rods, then, had to be spaced out in the same way but the threaded rod at the bottom that holds them was JUST BARELY long enough to let this happen.

While not there yet, I anticipate having to modify the X endstop holder to match the standard print plate area.

brnrd Wrote:
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> I asked prusajr at IRC today and he said 405 mm
> for the x axis smooth rods works.

I just tried 405mm and it's still quite a bit too long. I'm thinking something around 385mm should work.

I'm just finishing a Prusa Iteration 2 build and I cut the X rods to 406 mm, then hammered them into the X axis end pieces and installed them to the Z axis by spacing the Z motor mounts a little bit away from the vertexes with separate sets of nuts. It looks good, there's some space on the threaded rods on both sides of the Z motor mounts. In fact, since the X axis smooth rods aren't really adjustable anymore, you have to adjust the Z rods to vertical by adjusting the spacing of the Z motor mounts. So in practice you can't just bolt the Z motor mounts to touch the top vertexes.

I have found the same, with the x rods, and im going to cut them so that I can have the z motor mounts close to the top rails.


ttsalo Wrote:
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> I'm just finishing a Prusa Iteration 2 build and I
> cut the X rods to 406 mm, then hammered them into
> the X axis end pieces and installed them to the Z
> axis by spacing the Z motor mounts a little bit
> away from the vertexes with separate sets of nuts.
> It looks good, there's some space on the threaded
> rods on both sides of the Z motor mounts. In fact,
> since the X axis smooth rods aren't really
> adjustable anymore, you have to adjust the Z rods
> to vertical by adjusting the spacing of the Z
> motor mounts. So in practice you can't just bolt
> the Z motor mounts to touch the top vertexes.

I just upgraded my Prusa Mendel's X axis to the iteration 2 version and have had trouble getting my Z smooth rods exactly parallel because of the fixed X smooth rod length... like other described above.... anyone found a good method to get everything spaced correctly and the Z rods perfectly upright and parallel?

Also, it seems the center spacing for the Z lead screw is slightly different on the Z motor mounts and the X ends as described here [github.com] has anyone had any trouble with this? The difference is just .5mm but it still seems to be giving me a little trouble on my Z axis (Z lead screw and Z smooth rod can't be perfectly parallel). Anyone know if this has been fixed yet? Or has anyone fixed the files themselves?

I also ran across these (http://www.thingiverse.com/thing:15156) adjustable Prusa v2 X ends by GregFrost that would probably help a lot with having to cut your X smooth rods exactly to length (and the fact that there doesn't seem to be a clear answer to what length they actually should be), anyone tried them?

daufhammer Wrote:
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> I just upgraded my Prusa Mendel's X axis to the
> iteration 2 version and have had trouble getting
> my Z smooth rods exactly parallel because of the
> fixed X smooth rod length... like other described
> above.... anyone found a good method to get
> everything spaced correctly and the Z rods
> perfectly upright and parallel?

Yes, just use separate nuts for the Z motor mounts. That way you can adjust the smooth rod upper ends by adjusting the positions of the motor mounts.

Some people have reported that the Z rod and lead screw spacing is a tiny bit different in the motor mount and X ends, but it apparently only matters with some types of motors. I didn't have any problems with the shorter 1A motors from Alltronics.

According to Gary Hodson's sketchup model of the old prusa, it looks like <401 mm x-rods should work if there is a washer + nut + washer between the z motor mounts and the frame vertexes. Also, the inside of your frame vertexes (with feet) would need to be 234mm apart. I think I'm figuring something incorrectly though, because 405mm looked much too long for my Prusa... So I just ended up doing the seperate nut trick.

I agree with "just use separate nuts for the Z motor mounts", but the vast majority current instructions mention doing it the other way. It would be better for beginners just to get the x-rods cut to the length which will work with the old prusa instructions.

To figure this out for sure... Can someone with a Prusa V1 measure this?: [imgur.com]

The measurement that is gotten + 38mm + 38mm (depth of the x end holes) will give us what the x rods need to be without using separate nuts. That's probably the length we should use for the Prusa V2 BOM (which still doesn't have rod lengths listed: [github.com]).

Edit: I found the following quote from someone else on the forum:

epochapex Wrote:
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> OK. I cut the bars to 400mm and was able to align
> them correctly.

Could someone else still confirm the distance between their idler and motor mount on a Prusa V1?

Edited 1 time(s). Last edit at 03/23/2012 10:04PM by Pawl.

I just put my frame together using the standard length for the smooth rods: 420 mm for x, 406 mm for y and 350 mm for z. FIrst, I cut my threaded rods precisely,,and I placed the nuts so that they were flush with the ends everywhere to give me the maximum sized frame. I found that the spacing between the left and right vertices was 251 mm and decided to keep it since this would provide me with better clearance for the extruder in the x direction at high z. When I measured out the length for the smooth rods for this frame, I found that 420 mm is the correct length.

brnrd Wrote:
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> I placed the nuts so that they
> were flush with the ends everywhere to give me the
> maximum sized frame.

I'm a bit confused, so there are 2 washers and 2 nuts between your z-motor mounts and frame vertexes? I'm more interested in the length required when using 2 washers and 1 nut, so we don't have to depreciate old instructions.

Also, I'm thinking the BOM should say 400mm or 420mm smooth x-rods.

My z-motor mounts are in the bottom of the frame instead of the top. I do have a washer, nut, and two washers between each rod clamp and the z motor mount. Since the vertex is thinner than the rod clamps, you have to probably add another washer.

I think 405 or 406 mm is the length for the x smooth rods that you will need if you space the vertices at the recommended distance of 234 mm.


But when I do the math, I calculate 401 mm for the x smooth rods:

vertex spacing difference: 251 mm- 232 mm = 19 mm
x smooth rod length for std spacing of 232 mm: 420 - 19 = 401 mm

Edited 1 time(s). Last edit at 03/24/2012 10:49PM by brnrd.